1. Field of the Invention
The present invention relates to a roll machining apparatus for machining the surface of a roll while supporting and rotating the roll in a horizontal position, and more particularly to a roll machining apparatus for machining a roll into a machined product which requires precision machining, such as a roll mold for the production of, for example, an optical film for use in a liquid crystal display or a lenticular lens for use in a rear projection device.
2. Background Art
A roll mold as described above requires fine, very high-precision machining. Therefore, when machining a roll into such a roll mold, it is necessary to precisely support the roll while suppressing shaking, displacement of the axis, etc. of the roll during its rotation. For this purpose, it is preferred to support spindles, supporting the both ends of the roll, by means of hydrostatic bearings.
However, when a spindle is supported by a hydrostatic thrust bearing which receives a thrust load, because of small bearing gap of the bearing, the bearing cannot absorb thermal expansion of a roll in the length direction e.g. due to a change in room temperature, especially when the roll has a large length, causing scuffing in the bearing.
Japanese Patent Laid-Open Publication No. 11-207503 discloses an apparatus for machining a crankshaft as a workpiece, in which the both ends of the workpiece are supported by two spindles which are supported by hydrostatic bearings both in the radical direction and in the thrust direction. The workpiece is not directly fixed to one of the spindles, but fixed at its one end to a piston provided in the one spindle. The workpiece is supported with a tensile force applied to the one end from the piston.
Though the disclosed method makes it possible to absorb thermal expansion of a workpiece in the length direction e.g. due to a change in room temperature, involves a complicated structure of the apparatus. In addition, since one end of the workpiece is not directly fixed to the spindle, but fixed to the spindle indirectly via the piston, the workpiece cannot be supported stably, and shaking, displacement of the axis, etc. of the workpiece during its rotation are likely to occur.